1. Field of the Invention
This invention relates to optical systems, and more specifically, to an optical system that detects very fine three-dimensional surface features.
2. Description of the Related Art
The optical systems described in the above-incorporated U.S. patent application as well as other resonator-enhanced optical inspection systems, storage devices and other optical systems, such as those described by U.S. Pat. Nos. 6,700,840, 6,714,295, 6,717,707, 6,778,307 issued to Applicant Clark and others, the specifications of which are incorporated herein by reference, provide improved resolution, surface height detection and other performance improvements in traditional optical inspection systems and provide new types of optical systems that were not available prior to the inventions disclosed therein. Specifically, the incorporation of a Fabry-Perot resonator in the above-mentioned optical systems has increased the sensitivity of a particular measurement parameter via the resonance effects, and further made it possible to detect surface feature height using an intensity detector, whereas an external interferometer was previously required for the measurement.
Although each of the systems described in the above-referenced patents and in the above-incorporated parent application can measure the characteristics of a region, the measured characteristics are generally “lumped” in a single detector output and then the illumination and/or resonator is scanned across the surface of interest in order to determine the size and position of surface features.
In general, resonators are defined by a theoretically infinite number of reflections between multiple reflectors forming the resonant cavity. If a surface under measurement is one of the mirrors and exhibits surface variations, the resonance will cease to exist and the system becomes a multiple fringe interferometer. Multiple fringe interferometers can be used to provide topographic maps of a measured surface, but the resolution of the interferometer is limited by the number of reflections, which is dependent on surface variations as pointed out above. The resolution of the multiple fringe interferometer is also limited by the relatively small separation between the reflectors in order prevent loss of light energy due to angular variations.
Therefore, it would be desirable to provide further refinements in the optical systems described in the above-incorporated parent application and in other optical systems that can accurately measure the height and position of surface features while maintaining resonance independent of surface variations.